"And when your Lord declared" - al-Hasan said: meaning, your Lord made it known, "that He would surely continue to send against them until the Day of Resurrection those who would afflict them with" - meaning, those who would impose upon them, "the worst torment" - meaning, its severity.

Qatadah said: So He sent the Arabs against them, and they are, because of this, in torment through the jizyah (poll tax) and humiliation.

"Indeed, your Lord is swift in penalty" - al-Hasan said: When Allah intends to punish a people, His punishment of them is swifter than the blink of an eye.

"And indeed, He is Forgiving, Merciful" - to those who repent and believe.